Sound is a physical disturbance in the medium through which it propagates. For example, in air, sound consists of localized variations in pressure above and below normal atmospheric pressure. Accordingly, the vast majority of sound reproduction systems are comprised of electromagnetic transducers in which an electrical signal is transformed into a mechanical vibration which, in turn, is transformed into an acoustic signal. Sound reproduction systems typically include separate loudspeakers, each generating sound within a selected frequency range. For lower frequencies, i.e., frequencies below 300 Hz., loudspeakers are typically comprised of a diaphragm, most commonly, a relatively large cone, a support system in which the cone or other diaphragm is mounted and a driver which vibrates the cone in a desired fashion to produce sound waves. For higher frequencies, i.e., frequencies above 300 Hz., horn loudspeakers, which are characterized by a smaller cone or other type of driver and speaker walls, positioned forward of the cone, which follow a selected pattern are more common.
While sound reproduction systems have been the subject of numerous innovations over the years, pattern control of sound projection within a particular listening area has remained a problem. Effective pattern control is particularly problematic when the sound reproduction system is installed in a stadium or other large structure. While it would be very desirable to provide even sound levels throughout the stadium, various considerations has made such a goal quite difficult. One problem is the dramatic variation between the distance separating the closest and furthermost listeners from the stage. Specifically, while the closest listener may be just a few meters from the stage, the furthermost listener may be as far as 300 meters away. Thus, sound reproduction systems suitable for use in stadiums and other large venues must be capable of throwing sound considerable distances. As sound levels for high frequency sounds tend to drop off dramatically over distance, in order for high frequency sounds to travel these distances, the initial sound levels produced by the sound reproduction system must be quite high. For this reason, many sound reproduction systems capable of generating desired audible sound levels at the furthermost reaches of the stadium inadvertently produce sound far in excess of the desired audible sound levels close to the stage.
A common sound reproduction system used in stadiums and other large venues is generally referred to as a cluster system. Cluster systems are generally characterized by high efficiency, middle and high frequency range speakers having sharp vertical and horizontal directivity and high-power low frequency range speakers. In a cluster system, speakers are concentrated in one or two locations within the stadium or other large venue. While the location of a cluster system within a stadium or other large venue will vary depending on the particular uses contemplated therefor, in order for the cluster system to throw sound the requisite distances, cluster systems are typically elevated on the order of about 20 to 30 feet above their surroundings.
A variety of problems are caused by the design of cluster systems. While low frequency range sounds are generally omni-directional and can propagate, away from the cluster, in all directions, high frequency range sounds are highly directionalized and tend to propagate away from the cluster system in defined "beams" of sound. As a result, therefore, sound levels for high frequency range sounds tend to drop off dramatically outside the beam. Other problems are caused by the cluster system's use of multiple mid and/or high frequency range loudspeakers. For both of these frequency ranges, cluster systems typically include a horizontal array of loudspeakers. Typically each loudspeaker is directionalized to provide acoustical coverage for a selected portion along the horizontal plane. However, the coverage areas of adjacent loudspeakers often overlap, thereby causing a variety of interference problems. Overlap of coverage areas is of particular concern when the loudspeakers are placed in proximity to each other. Thus, the design of a compact, space-efficient array of mid or high frequency loudspeakers which provides uniform coverage in the horizontal plane remains problematic.